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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
/**
@file rsa_exptmod.c
RSA LTC_PKCS exptmod, Tom St Denis
*/
#ifdef LTC_MRSA
/**
Compute an RSA modular exponentiation
@param in The input data to send into RSA
@param inlen The length of the input (octets)
@param out [out] The destination
@param outlen [in/out] The max size and resulting size of the output
@param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC
@param key The RSA key to use
@return CRYPT_OK if successful
*/
int rsa_exptmod(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen, int which,
rsa_key *key)
{
void *tmp, *tmpa, *tmpb;
unsigned long x;
int err;
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(key != NULL);
/* is the key of the right type for the operation? */
if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
return CRYPT_PK_NOT_PRIVATE;
}
/* must be a private or public operation */
if (which != PK_PRIVATE && which != PK_PUBLIC) {
return CRYPT_PK_INVALID_TYPE;
}
/* init and copy into tmp */
if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != CRYPT_OK) { return err; }
if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto error; }
/* sanity check on the input */
if (mp_cmp(key->N, tmp) == LTC_MP_LT) {
err = CRYPT_PK_INVALID_SIZE;
goto error;
}
/* are we using the private exponent and is the key optimized? */
if (which == PK_PRIVATE) {
/* tmpa = tmp^dP mod p */
if ((err = mp_exptmod(tmp, key->dP, key->p, tmpa)) != CRYPT_OK) { goto error; }
/* tmpb = tmp^dQ mod q */
if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK) { goto error; }
/* tmp = (tmpa - tmpb) * qInv (mod p) */
if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK) { goto error; }
if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK) { goto error; }
/* tmp = tmpb + q * tmp */
if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK) { goto error; }
if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK) { goto error; }
} else {
/* exptmod it */
if ((err = mp_exptmod(tmp, key->e, key->N, tmp)) != CRYPT_OK) { goto error; }
}
/* read it back */
x = (unsigned long)mp_unsigned_bin_size(key->N);
if (x > *outlen) {
*outlen = x;
err = CRYPT_BUFFER_OVERFLOW;
goto error;
}
/* this should never happen ... */
if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) {
err = CRYPT_ERROR;
goto error;
}
*outlen = x;
/* convert it */
zeromem(out, x);
if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK) { goto error; }
/* clean up and return */
err = CRYPT_OK;
error:
mp_clear_multi(tmp, tmpa, tmpb, NULL);
return err;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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